Electrical system



Oct. 8, 1940. J. PLEBANSKI 2,215,329

' ELECTRICAL SYSTEM Filed April 11, 1936 2 Sheets-S heet 1 INVENTOR.

ATTORNEY.

Oct. 8, 1940. J, E N 2,216,829

ELECTRICAL SYSTEM Filed April 11, 1936 2 Sheets-Sheet 2 To AVC INVENTOR.figw #1 26115 m/ L BY 7 MM fin.

ATTORNEY.

Patented Oct. 8, 1940 PATENT OFFICE ELECTRICAL SYSTEM J ozei'.Plebanski, Warsa w, Poland, assignor to Radio Patents Corporation, NewYork, N. Y., a corporation of New York Application April 11, 1936,Serial No. 73,865 In Poland April 26, 1935 1 Claim. (01. 250-40) Mypresent invention is concerned with the provision of a system for and amethod of varying the reactive impedance in an alternating currentcircuit without using a mechanically adjustable variable reactanceelement such as a variable capacitor or a variable reactor.

One object of the invention is the provision of means for and a methodof varying the apparent reactance in an alternating current circuitpurely electrically by the adjustment or variation of an auxiliaryelectric current or potential.

Another object is to vary the apparent capacitative reactance in analternating current circuit purely electrically by the adjustment orvariation of an auxiliary electrical current or potential.

A further object is to vary the apparent inductive reactance in analternating current circuit purely electrically by the variation of anauxiliary electrical current or potential.

Another object is the provision of means for and a method of varying thecapacitative and inductive reactance in an alternating current circuitwithin a wide range from positive to nega-. tive reactance values.

Another object is to provide a means for and a method of varying thetuning of an oscillatory circuit purely electrically by adjusting anelectric current or potential.

A further object is to increase the apparent inductive reactance of achoke coil without increase of its physical characteristics anddimensions.

Another object is to control the phase angle in an alternating currentcircuit by purely electrical means for power correction purposes and thelike.

The invention has other objects in view which will appear hereafter inthe detailed description thereof in connection with the accompanyingdrawings in which I have shown and illustrated by way of example severalpractical embodiments and methods for practising the invention.

In the drawings wherein similar reference numerals identify similarparts throughout, Figure 1 illustrates a basic circuit arrangementaccording to the invention for controlling the inductive reactance in analternating current system. Figure 2 is a similar arrangement adaptedfor control of the capacitative reactance. Figure 3 is a circuitcombining the arrangements of both Figures 1 and 2. Figures 4 and 5illustrate alternative arrangements to Figures 1 and 2. Figure 6 is atheoretical diagram explanatory of the function of the circuits; Figure7 illustrates an example of the invention as embodied in an oscillator.Figure 8 illustrates the invention embodied in a radio receiver. Figure9 illustrates a modification of a radio receiver embodying theinvention. Figure 10 illustrates a rectifying and smoothing system withthe inventive circuit embodied therein. Figure 11 shows the inventionembodied in a power system for power factor 6 correction. I

With the above mentioned objects in view, the invention in generalinvolves the provision of a regenerative circuit comprising an amplifiersuch as a vacuum tube amplifier or equivalent device 10 having anoperating or main circuit associated with its input, and a reaction orfeedback circuit arrangement for reacting amplified output energy uponthe main or input circuit. In contradistinction to the usualregenerative systems known 15 in the art wherein the feedback potentialis either in phase or 180 out of phase with the non-reactive potentialin the main or input circuit resulting in an increase or decrease of theapparent non-reactive impedance or resistance of the cirm cuit, Iprovide in accordance with the improvements of the present inventionmeans associated with either the input or output circuit of theamplifier for shifting the phase of the feedback potential so as to beequal or dephased by 180 with the reactive potential in the input ormain circuit; that is, with either the capacitative or inductivepotential. In other words, in the ordinary regenerative circuit thereacting potential is in phase with the current or non-reactivepotential drop resulting in an apparent increase or decrease of thenon-reactive or loss resistance of the circuit. In an arrangement of thetype according to the invention on the other hand, the reactingpotential is in phase with the reactive potential drop in the circuit,or in other words, in phase quadrature either leading 01 lagging withthe current flowing in the circuit. In this manner the apparent reactiveimpedance that is either the inductance or capacitance of the maincircuit is varied resulting in a corresponding increase or decrease ofthe resultant eifective reactance in the circuit.

Referring to Figure 1 of the drawings, I have shown a basic circuit ofthis character. Numeral 3 represents an inductance coil forming a tankcircuit together with a condenser 4 and a resistance 5 and supplied withalternating current energy from a suitable source shown at l by means ofa coupling coil 2. Item 6 illustrates an amplifying valve or equivalentdevice such as a vacuum tube amplifier having its grid-cathode pathconnected across the opposite ends of the resistance 5 and including afeedback or tickler coil in its output circuit arranged in inductive 5'coupling relation with the inductance coil 3 of the main or inputcircuit. The valve 6 is connected in the usual manner to a high tensionsource as indicated by the plus and minus symbols.

In an arrangement of this character, it can be shown that the potentialinduced by the coil 1 in the circuit 3, 4, is in phase quadrature withthe current in the circuit in such a manner that the effect of theinduced or reacting potential is equivalent to an increase or decreaseof the apparent inductance of the circuit. As is understood, any othersuitable means for shifting the phase of the reaction currents maybeprovided. Thus the resistance 5 may be omitted and the cathode grid pathof the tube connected across the condenser 4 in the usual manner and asuitable phase shift device inserted in series with the reaction coil 1to produce the desired dephasing.

Referring to Figure 2, this shows an equivalent arrangement for increaseor decrease of the capacitative reactance of the circuit 3, 4, 5. Tothis end I have shown a feedback capacity connected between the anode ofthe valve 5 and the input circuit. The grid of the valve may be suitablybiased in a well known manner such as by means of a resistance 9inserted in the cathode lead and shunted by the condenser 10. I havealso shown a modified coupling arrangement from the resistance 5 to thegrid of the valve 6 comprising a coupling condenser H and grid leakresistance ll of known design. In order to effect a gradual increase ordecrease of the apparent capacitance of the circuit I have shown thecenter point of the resistance 5 connected to ground or negativepotential and a variable contact l2 cooperating with the resistance 5for adjusting the control potential applied to the grid of the valve. Inthe example shown, if the contact i2 is moved in the direction to theright from the center point l3, the apparent capacitative reactance ofthe circuit is increased, and vice versa, by moving the contact l2 in adirection towards the left from the point IS, the apparent capacitativereactance of the circuit decreases. Item l4 represents a drop resistancein the anode lead for securing the proper anode potential for the valvein a manner well known.

Figure 3 shows a circuit combining the arrangements of Figures 1 and 2for simultaneously varying both the apparent or virtual capacitative andinductive reactance.

The behavior and function of the circuit described is further explainedby the following. Assuming S to be a coefficient depending on thecharacteristics of the valve 6, and assuming further for simplicity thatthe valve has a linear grid voltage-anode current operatingcharacteristic. then the theoretical equation for the circuit 3, 4, 5will be as follows wherein i represents the current in the circuit, Rthe value of the resistance 5, L self inductance of the coil 3, M theco-efficient of mutual inductance between the coils 3 and l, C thecapacicircuit.

provides a means for artificially introducing into a circuit a positiveor negative inductance (iMR S) or a positive or negative capacitance C3ts which may be either added or subtracted from the real inductance L orthe real capacity C of the circuit. By this method it is possible tovary the tuning of the circuit in a simple manner such as by adjustingthe contact l2 within wide limits without changing the inductance coiland without range switching required in tuning methods known in the art.

The tuning of the circuit 3 4, 5 can be effected in various manners by avibration of the amplification or gain of the valve 6, such as byvariation of grid voltage as shown in the drawings or by varying thescreen grid potential, the anode potential or by any other gain controlmethod.

It is furthermore possible by using a system described by the inventionto secure a negative inductance or capacity if the negative feedbackpotential is greater than the corresponding positive reactive potentialin the circuit in a manner similar to the creation of a negativeresistance obtained by the ordinary methods of regeneration heretoforeknown in the art. Such a circuit with a negative reactance that iseither negative" inductance or negative capacitance behaves in just theopposite manner to similar circuits with respective positive circuitconstants. Thus, as is well known, a circuit with positive inductanceand capacity will become a self oscillator if the resistance in thecircuit is negative." A circuit with negative inductance and capacityhowever will oscillate only if the resistance in the circuit ispositive, but will not oscillate if the resistance is negative." Theresonance curve of such a negative circuit, that is a circuit in whichboth inductance capacitance and resistance are negative, is nearly thesame as for a positive circuit in which both inductance capacitance andresistance are positive, the only differ- -ence consisting in adephasing of the currents Referring to Figure 6, I have illustrated aresonance curve showing the current i in a positive circuit as afunction of the angular velocity and the phase angle therefor 2 thesecurves being well known to those skilled in the art. represents thephase angle for a negative circuit and 4p" the phase angle for a circuithaving both negative inductance and capacitance but positive resistance.A circuit of the latter type will become an oscillator in a mannersimilar as a circuit with both positive inductance and capacitance andnegative resistance.

As will be understood, it is further possible by means of an arrangementaccording to the invention to secure practically zero capacity orinductance in a circuit. In the former case the inherent capacity of aself inductance coil can be completely balanced by a correspondingnegative capacity supplied by means of a tuning valve in a system asdescribed. Such a circuit or coil will develop a maximum A. C. potentialat its terminais.

The invention has also great uses in short wave systems as is understoodwhere comparatively small capacities are required which have to beadjusted gradually and within very fine limits. Tuned coils withcompensated inherent capacity may also be provided with great advantagein radio receivers to secure maximum amplification 1 the art.

ratio as the amplifying valve 30 amplifies the and maximum selectivityespecially for the shorter wave lengths.

Referring to Figure 7, I have shown a vacuum tube oscillator for use ina transmitter and the like provided with a purely electrical tuningsystem according to the invention. The oscillator shown comprises avalve 20 of the self-oscillating type having a grid tank circuit 3, 4, 5in which sustained oscillations are maintained by a regenerativearrangement of any known type such as a feedback coil 2| inserted in theanode circuit. The valve 6 which serves as the tuning valve has itsgrid-cathode path connected to a portion of the resistance 5 in a mannersimilar as described in the previous figures and a feedback coil 1inserted in its anode circuit and inductively coupled with theinductance coil 3 of the oscillating circuit. In this manner it ispossible to adjust the tuning or wave length of the circuit 3, 4, 5 byvarying the amplification of the valve 6 such as by adjustment of thevariable contact of the resistance 5. The oscillations produced in thecircuit 3, 4, 5 may be transmitted to an output or utilization circuitsuch as a transmitting antenna wire line, etc., through the couplingcoil 2.

Referring to Figure 8, this illustrates the invention embodied in aradio receiving system for tuning a receiver to the wave length of atransmitting station. Item represents a receiving antenna connected inseries with an antenna coupling condenser 26, a tank circuit comprisedof an inductance 28 and a condenser 29 in parallel and ground 33 in theusual manner known in The receiving currents set up in the tank circuit28, 29 are applied to the control grid of an amplifying tube suppliedfrom a suitable high tension source as indicated by the symbol. The gridof the tube is negatively biased by the provision of a voltage dropresistance 3| in the cathodelead shunted by a condenser 32. Item 35represents a high frequency choke coil connected between the anode ofthe tube 30 and the high tension source and serving to develop highsignal potential variations at theanode to be applied toa followingstage of amplification connected between points a and b through acoupling condenser 34. In order to tune the circuit 28, 29 to the wavelength of a desired transmitter, I have shown a tuning system of thecharacter as previously described comprising a tuning valve forcontrolling the apparent reactance of the circuit 28, 29. To. this endthe tuning valve 40 has its grid-cathode path connected to a portion ofa resistance 39 included in a resonant input circuit comprised of aninductance 31 and condenser 38 and controlled from the output of thevalve 30 through the coupling condenser 34. Items 4| and 42 represent aresistance and shunt condenser inserted in the cathode lead of the valve40 for securing proper negative grid bias. The anode circuit of thevalve 40 connected to the positive pole of the high potential sourceincludes a pair of feedback coils 36 and 44 arranged in inductivecoupling relation with the inductance 31 and 23 of the input circuitsfor the valves 40 and 30 respectively. In the example shown, thefeedback coils 36 and 44 are connected in parallel, the latter furtherhaving a resistance 43 in series therewith. In this manner, bothcircuits 28, 29 and 31, 38 may be tuned by a single control operation,such as by adjusting the variable contact of the resistance 39. Thevalue of the resistance 43 should be chosen in such a manner as todecrease the current of the tuning valve 40 in the same signallingcurrents.

Referring to Figure 9, I have shown a radio receiving system wherein aseparate tuning valve is provided for each amplifying stage. Theamplifying and tuning valves are shown enclosed in a common envelope ina manner similar to the known multi-purpose valves now being used. Inthe circuit two amplifying stages have been shown, the first stagecomprising a composite amplifying and tuning valve 50, and the secondstage comprising a composite valve 60. The valve 50 has a commoncathode, a pair of grids 5| and 52, and a pair of anodes 53 and 54arranged in a suitable manner such as known in the construction ofmulti-purpose valves. The cathode, grid 5| and the anode 53 form theamplifying section and the cathode, grid 52 and anode 54 form the tuningsection. Similarly the valve 60 comprises a cathode, a pair of grids GIand 62, and pair of anodes 63 and 64, the cathode, grid GI and anode 63forming the amplifying section and the oathode, grid 62 and anode 64forming the tuning section. A circuit of the character according toFigure 9 is well suited for securing automatic volume control as will bedescribed later.

The antenna circuit includes a resonant or tank circuit comprising aself inductance 41 shunted by a capacity 48 in series with a resistance49. The cathodes of the tubes 50 and 60 are shown connected to ground 33or negative reference point of the system through voltage drop resisters45 and 61 shunted by condensers 45 and 58 respectively. The tuned inputcircuit 41, 48 is shown directly connected across the grid-cathode pathof the amplifying section of the tube 5U through a suitable couplingdevice for introducing an automatic volume control potential (indicatedat AVC), and the grid 52 of the tuning section of the valve is connectedto the junction point of the condenser 48 and the resistance 49 of theresonant circuit in a manner similar as described in the precedingfigures. The anode 53 of the tube 50 is shown connected to the positiveterminal of a high potential source through a high frequency couplingchoke 53 while the anode 54 of the tuning section of valve 50 is shownconnected to the positive pole of the high tension source in series witha voltage drop resistance 56 and a feedback coil 55 in inductivecoupling relation with inductance 41 of the resonant input circuit. Item51 is a decoupling condenser for the resistance 56 connected between itslower end and ground. The signal potential variations developed at theanode 53 are applied to the valve 60 through a coupling condenser 51' inthe manner similar as described in Figure 8. The resonant circuit forthe valve 60 comprises an inductance 55 shunted by a condenser in serieswith a resistance 66. The grid iii of the amplifying section of tube 60is connected to the upper terminal of the resonant circuit while thegrid 62 of the tuning section of valve 60 is connected to the junctionbetween the condenser 65 and the resistance 66. The anode 63 of theamplifying section is' connected to the positive pole of the hightension source through the coupling choke coil 63' similar to the chokesistance 56 forms a common part of the anode circuits of both tuningsections of valves 50 and 60 and serves for varying the anode potentialsapplied to the tuning sections to vary the amplification and accordinglythe degree of wattless reaction upon the resonant circuits 4T, 48, 59and 65. In this manner the circuits are simultaneously tuned by a singleor unicontrol element common to all tuning valves (resistance 56). Thetuning resistance may be made in the form of a long fiat spiral providedwith a sliding contact adapted to short circuit a part of theresistance. In this manner an easy and accurate tuning can be effectedover a comparatively wide range of wave lengths without requiring anyrange switching operations. The signal potential developed at the anode63 may be utilized in any desired manner through a coupling condenser 64and applied to a further amplifier stage or any other translating deviceconnected to points a and b, as the case may be.

As described hereinbefore, the reactive regeneration is obtained byinserting an ohmic resistance in the resonant circuit to secure a 90dephasing of the reacting potential. As pointed out, any other phaseshift arrangement may be used in connection with the invention. If thegrid is coupled to the resonant circuit in the ordinary manner and aphase shift device is included in the anode circuit, the latter shouldbe of such construction as to insure an even phase shift of 90 for awide band of frequencies if it is desired to use the system for tuningpurposes.

The alternative arrangement for securing a 90 phase shift of thereacting potential is shown in Figures 4 and 5. In the latter theresonant circuit is connected with the grid-cathode path of the tuningvalve in the usual manner and the reacting or feedback path from theanode circuit connected to such a point in the resonant circuit so as tosecure the required phase quadrature between the current and thereacting potential. Thus, according to Figure 4, the feedback pathincluding a condenser 8 is connected to the junction between theinductance 3 and resistance 5 and in the arrangement according to Figure5, the anode of the tuning valve is connected to the junction betweenthe condenser 4 and resistance 5 with a suitable bi-pass condenser 4'connected between the remaining end of the resistance 5 and theinductance 3.

The resistance 5 may have a small value. Assuming R0 to be the totalloss resistance of the resonant circuit, the insertion of the additionalresistance has for its object only to secure an ohmic potential dropimpressed upon the grid control of the tuning valve. The total ohmicdrop at resonance is therefore equal to I (RH-R) where I is the currentflowing in the circuit. This total drop is equal to E which is theelectromotive force acting in the circuit. As is understood, it is neverpossible to secure a greater grid potential than E, and not even thisvalue on account of the drop through the resistance 5. The latter shouldtherefore be greater or equal than R0 whereby the maximum potentialavailable for the tuning valve is equal to or greater than E/2. Thus, ifR0 is equal at 10 ohms, R1 may be also 10 ohms or 20 ohms or more.

The provision of the resistance 5 increases the damping of the circuit.This drawback however may be minimized or eliminated by reducing theapparent capacity and/0r increasing the apparent inductance of thecircuit by the method in such a manner that the damping is considerably'reduced to offset the effect of the additional resistance 5 since thedamping in the circuit is proportional to C and R and inverselyproportional to the inductance L as is well known to those skilled inthe art.

By using a system as described by the-invention, it is possible tosecure circuits having such a low damping as it is otherwise impossibleto obtain, especially for the higher frequencies by decreasing theapparent capacity and increasing the apparent inductance to extremelysmall and large values respectively.

As is understood from the above, the invention has manifold'other uses,and may serve for frequency modulation, phase modulation, or in general,for any system or method utilizing or based on a variable reactance inan alternating current circuit. Thus, for instance, the system describedin Figure 7 may be used for producing a frequency modulated outputcurrent by varying the amplification of the tuning valve 6 in accordancewith a modulating signal such as by means of an audio transformer l6having a secondary inserted in the grid circuit and a primary connectedto the output of a suitable modulating source such as a microphonecircuit or the like.

Referring to Figure 10, I have illustrated a further embodiment of theinvention as applied to a rectifying system for producing substantiallysteady direct current from an alternating current source. The systemdisclosed comprises the usual elements of an alternating current sourceshown at l, a rectifying system 12 in the example shown comprising fourrectifying devices such as heavy current metal rectifiers arranged in aWheatstone bridge in a known manner with one diagonal branch of thebridge circuit connected to the input or alternating current circuitthrough a transformer having a primary 10 and secondary H and with theremaining diagonal branch connected to a load indicated at 16 through asmoothing filter. The latter, in the example shown comprises a seriesinductance coil 14 and a pair of parallel condensers I3 and 15. Whenusing a system of this type for supplying heavyrectified currents, thedimensions of the smoothing filter, especially the choke coil 1|,necessary for securing a steady and smooth output current and the costsbecome prohibitive for most practical cases. This drawback can beovercome in the arrangement shown by a system for increasing theapparent inductance as described by the invention and comprising in theexample shown a reaction valve 19 which may be either a high vacuum or agas filled valve and has its grid controlled from the load or outputcircuit of the rectifier through a usual coupling arrangement comprisinga coupling condenser BI and grid leak resistance 82. Items 80 and BIrepresent the usual voltage drop resistance and shunt condenser insertedin the cathode lead for securing the desired negative grid bias. Theanode of the reaction valve 19 is shown to be supplied from a separatehigh tension source comprising a one-way rectifier 84 connected to theinput circuit through an auxiliary transformer winding 83 of the primaryI0 and in series with a suitable smoothing filter comprising a serieschoke coil 85 and parallel condensers 86 and 86' and a feedback orreaction coil 18 in inductive coupling relation with the filter chokecoil H. The filter coils 85, 86 have considerably smaller dimensionsthan the choke coil 14, since the current through the reaction valve hasa considerably smaller value compared with the output current of therectifier. In this manner the apparent inductance of the choke coil 14may be increased to considerable values suited for smoothing out heavydirect currents without prohibitive increase of size and cost ofapparatus required.

Referring to Figure 11, this illustrates another example of practisingthe invention relating-to the correction or compensation of the powerfactor in an alternating current system. I have again shown analternating current source which may be an ordinary power circuit or network supplying an inductive load indicated at 90, The correcting systemfor applying a leading current to the circuit for compensating theinductive or lagging current caused by the load is shown to comprise asmall series resistance 99 connected across the grid-cathode path of areaction valve 94 to secure the desired 90 phase shift similar asdescribed in the preceding examples. Items 95 and 96 are the usual dropresistance and parallel condenser inserted in the cathode lead forsecuring proper negative grid bias. The anode circuit of the valve 94includes a reaction inductance coil 92 arranged in inductive relationwith an inductance coil 9| connected in theprimary or main circuit thepower factor of which is to be corrected. The anode potential for thevalve 94 is supplied by a,separate source comprising a one-way rectifier98 connected to the main circuit through a transformer 91 and includinga smoothing filter comprising a series choke coil I00 and parallelcondensers I01 and I02. In the example illustrated, the compensatingtransformer 9|, 92 is connected in parallel to the source I or load 90and it is understood that similar results areobtained by connecting theprimary 9| in series with the circuit.

As is'evident from the above, the invention is not limited to'thespecific embodiments disclosed and described, but the underlyingprinciple is susceptible to numerous variations and modificationsdiffering from the exemplification shown and described herein forillustration in accordance with the broadest scope and principle of theinvention as defined in the appended claim.

I claim:

A radio circuit comprising a first valve, a resonant input circuit andan output circuit therefor, a second valve, a second resonant circuitconnecting the output circuit of said first valve with the input of saidsecond valve, said second resonant circuit including a non-reactiveimpedance element in series for supplying the control potentialfor saidsecond valve, feedback circuit paths from the output of said secondvalve to said resonant circuits, and rfieans for controlling theamplifying gain of said second valve.

JOZEF PLEBANSKI.

